The invention relates to a projection device comprising a projection screen, at least one radiation source and at least one monochrome display device for operation in the transmission mode, the display device comprising electro-optical means between two parallel substrates provided with drive means to cause the electro-optical means to change its transmission state at least locally and to define a pattern in the electro-optical means, projection means for projecting the pattern onto the projection screen.
The electro-optical means may be one of the many liquid crystalline materials, but alternatively the display device may be an electroscopic display.
The invention also relates to a display device and to an illumination source, both of which can be used in such a projection device, but which are alternatively usable for other applications.
It has been proposed quite frequently to replace the cathode ray tube in projection television devices with other display elements such as, for example LCD's. An example of such a device is given in the article "LCD Fullcolor Video Projector," by S. Morozumi et al., in SID '86, Digest, pages 375-378. The device shown in this article has a white light source, two dichroic mirrors, three LCD-display elements (light valves), one dichroic prism and a projection lens with an associated screen. The light from the source is split into three sub-beams (red, green, blue) and each beam passes an associated liquid crystal cell which serves as a light switch. After traversing the light switches, the three sub-pictures thus obtained are combined and imaged on the projection screen.
A problem in such a projection device is that the white light source has a wide spectrum of emitted radiation. In the optical set-up of the system, this gives rise to an incomplete split-up into the three primary colours (red, green, blue) and to chromatic aberration in the image on the projection screen.
It is an object of the invention to obviate these drawbacks.